This invention relates to electric drive circuits for powering spacecraft thrust engines including arc-jet engines and ion engines and, more particularly, to a drive circuit adapted for employing voltages supplied by solar panels of a spacecraft for application directly to the electrodes of the engine.
The engines which drive a spacecraft are in the nature of a thruster emitting a stream of high-velocity particles which accelerate the spacecraft in a desired direction as may be required for adjustment of the spacecraft position or orientation during station keeping, as well as for adjustment of the spacecraft orbit. An arc-jet engine and an ion engine are examples of typical thrusters in common use.
Both the arc-jet and the ion engines employ a gas which is electrically charged by an input power source to produce a plasma of high speed electric particles. In the arc-jet engine, the intense heat of the plasma results in an acceleration of particles out of the mouth of the thruster with a corresponding force being developed against the spacecraft to drive the spacecraft in a desired direction. In the ion engine, an electrode grid structure applies an accelerating voltage to the charged particles to accelerate the particles out of the mouth of the thruster to develop the force which drives the spacecraft in the desired direction.
The operation of such thrust engines requires both high voltage and a relatively low voltage. The high voltage is required to initiate electric conduction through the gas of the engine to produce the plasma. Thereafter, electrical conduction through the plasma can be maintained at the low voltage. The solar panels of a spacecraft are employed for generating the electric power necessary for operation of the thrust engine.
A problem arises in that the voltage outputted by a solar panel is too low for operation of the thrust engine. In the past, this problem has been addressed by interposing a DC-to-DC converter between the power source of the solar panels and the thrust engine to increase the voltage, at which the direct current (DC) is supplied by the solar panels, to a higher voltage suitable for operation of the thrust engine. This has the disadvantage of increasing the weight and the complexity of the electrical equipment carried by the spacecraft in contradiction to the general principle of minimizing the weight and the complexity of spacecraft.